Motor cooling system

ABSTRACT

A motor cooling system in which the stator (1) of a motor is coated with a coating layer (11), and a cooling liquid is applied to the projecting portions (10) of stator coils and to the side portions of the rotor (2) to cool the motor. The motor cooling system is advantageously applicable to a spindle motor for a machine tool.

TECHNICAL FIELD

The present invention relates to a motor cooling system, and, moreparticularly, to a motor cooling system advantageously applicable tocooling a spindle motor for a machine tool.

BACKGROUND ART

Self-cooling type motors are usually equipped with an individual fanmotor at the rear end thereof, but a spindle motor for rotativelydriving the spindle (tool spindle) of a machine tool cannot besatisfactorily cooled by a self-cooling fan, because the spindle motoroperates over a wide speed range of from a low speed to a high speed.

Accordingly, as shown in FIG. 3, the conventional spindle motor isprovided, on the outer circumference of a stator 1, with an oil jacket 3having helical groove 31 formed in the outer circumference thereof andcovered with an outer sleeve 4, to form a path extending from an inletopening 30 formed on the outer sleeve 4 to an outlet opening 32 formedon the outer sleeve 4, and a cooling liquid is passed through the pathas indicated by arrows F₁ and F₂ to cool the oil jacket 3.

The conventional oil jacket cooling system cannot efficiently cool thestator, because this is an indirect cooling system which removes heattransferred, from the stator heated by the heat generated by the coils,projecting portions 10 of the to the oil jacket.

Furthermore, the conventional cooling system cannot remove heatgenerated in the rotor 2 and in end rings 20 attached respectively toopposite ends of the rotor 2 on the drive shaft 5.

The present invention provides a means which eliminates thedisadvantages of the conventional motor cooling system, and is capableof removing heat generated in the rotor and the stator coils.

DISCLOSURE OF THE INVENTION

As exemplified in FIG. 2, a stator 1 is processed by molding to apply acoating layer 11 of a synthetic resin over projecting portions 10 ofstator coils projecting from the opposite ends of a stator core and theresin coats a core of the stator, nozzles 9 are inserted through ahousing H in the interior of the spindle motor driven by drive shaft 5,a cooling liquid (or oil) L is sprayed by the nozzles 9 over the statorcoils and the end rings 20 of the rotor 2, and the cooling liquid L isdrained through outlet openings 92.

Thus, both the rotor and the stator coils coated with the syntheticresin can be directly cooled to increase the coefficient of heatconvection and the coefficient of cooling, whereby the motor can beefficiently cooled.

Since the cooling liquid can be applied directly to the heat generatingmembers, namely, the stator coils, the rotor and the end rings, theheating of the motor can be remarkably reduced compared with the heatingof the conventional motor, and the motor can be made more compact.

Efficient cooling makes it possible to reduce the size of the spindlemotor, and increase the output capacity by increasing the currentsupply, to thereby widen the output range of the spindle motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a motor employing a motor cooling systemin a first embodiment according to the present invention;

FIG. 2 is a schematic sectional view of a motor employing a motorcooling system in a second embodiment according to the presentinvention; and

FIG. 3 is a schematic sectional view of a motor employing a conventionalmotor cooling system.

BEST MODE OF CARRYING OUT THE INVENTION EXAMPLE 1

FIG. 1 shows a spindle motor having a stator length of 346 mm and astator outside diameter of 180 mm, to which the present invention isapplied. A stator 1 having stator coils with partly projecting portions10 which project from the opposite ends of a stator core and is coatedwith a layer of a synthetic resin 11 by molding and is finished bymachining the layer of the synthetic resin. A rotor 2 fixedly providedat opposite ends thereof with end rings 20 each coated with a syntheticresin coating 21 is combined with the stator 1 to construct a motorhaving a drive shaft 5. The motor is sealed in a watertight fashion byfitting an oil jacket 3 on the outer circumference of the stator, andfixedly attaching a front flange 6 and a rear housing 7 respectively toopposite ends of the oil jacket which is sealed with a sealing ring 8.

The oil jacket 3 is provided in the outer circumference thereof with ahelical groove 31, and an outer sleeve 4 is fitted on the outercircumference of the oil jacket 3 to define a path for a cooling liquidbetween the helical groove 31 and the inner circumference of the outersleeve 4. The opposite ends of the helical groove 31 are connectedrespectively to an inlet opening 30 and an outlet opening 32 formed inthe outer sleeve 4. Inlet openings 90 and outlet openings 92 are formedrespectively at opposite ends of the oil jacket 3 to form flow passages91 each extending from the inlet opening 90 through outer ends of thestator coils and the outer surface of the end ring 20 to the outletopening 92.

In operation, an oil (High-pressure Insulating Oil A, Nisseki K.K.)having a specific weight of 0.881, a viscosity of 7 cst and an ignitionpoint of 135° C. was injected into the interior of the motor at apressure of 0.7 kg/cm² through the inlet openings 30 and 90 of the oiljacket 3 to make the oil flow through a path F₁, F₂ extending from theinlet opening 30 via the helical groove 31 to the outlet opening 32, andthrough paths A₁, A₂ extending from the inlet opening 90 via the flowpassage 91 to the outlet opening 92.

Heat generated by the stator coils and transferred to the stator corewas conducted through the oil jacket to the oil flowing through thehelical groove 31, which carried away the heat. Heat generated byprojecting portions 10 of the stator coils projecting from the statorand heating the end rings 20 was absorbed and carried away by the oilflowing through the flow passages 91.

Since the projection portions 10 of the stator coils of the stator 1 arecoated with a synthetic resin coating layer 11, and the rotor 2 iscoated with a synthetic resin coating layer 21, the direct cooling ofthe motor by the oil did not cause any problem in the function of themotor.

EXAMPLE 2

As shown in FIG. 2, the motor of Example 2 is similar in construction tothe motor of Example 1 shown in FIG. 1, where the parts are presented bythe same numerals except that nozzles 9 are inserted through a fronthousing 6 and a rear flange 7 in the interior of the motor so that theextremities of the nozzles 9 are positioned near the projecting portions10 of the stator coils of a stator 1 and near the end rings 20 of arotor 2 to make the cooling oil L flow from the nozzles 9 to outletopenings 92, instead of the cooling paths extending from the inletopening 90 via the flow passage 91 to the outlet opening 92 in Example1.

In operation, a cooling oil (or liquid) L was jetted by a pressurizingdevice, not shown, through the nozzles 9 against the projecting portions10 of the stator coils and the end rings 20. The cooling oil L wasdrained through the outlet opening 92.

The projecting portions of the stator coils, and the end rings weredirectly cooled, and Example 2 had the same function and effect asExample 1.

Modifications

The oil employed as a cooling liquid may be replaced by cooling water,and the end rings of the rotor need not be coated with the syntheticresin layer to achieve the object of the object of the invention.

We claim:
 1. A motor cooling system comprising:a coating layer coatingprojecting portions of stator coils of a stator of the motor; a coolingliquid cooling said projecting portions of said stator coils and coolingopposite ends of a rotor of said motor; an oil jacket surrounding saidstator of the motor, said oil jacket having inlet and outlet openingsformed on opposite sides of the oil jacket; and flow passages extendingfrom the inlet opening, extending past the coating layer coating theprojecting portions of the stator coils, extending past outer surfacesof end rings of the rotor and extending to the outlet openings of theoil jacket, wherein the cooling liquid flows through the flow passages.2. A motor cooling system according to claim 1 wherein said oil jacketfurther comprises a helical groove provided on an outer circumferencethereof.
 3. A motor cooling system according to claim 2 furthercomprising an outer sleeve fitted on the outer circumference of the oiljacket, opposite ends of the helical groove connected respectively to aninlet opening and an outlet opening formed in the outer sleeve to definea second flow passage for the cooling liquid between the helical grooveand an inner circumference of the outer sleeve.
 4. A motor coolingsystem according to claim 1 further comprising a coating layer coatingouter surfaces of said end rings of said motor.